A Delhi court has acquitted a man of charges of raping and threatening a woman on the false promise of marriage, saying the complainant was "mature enough" to understand what was happening between them.

The court, while noting that the woman was already married to the accused but had concealed it in her complaint, also said her testimony was "not intrinsic worth believing to base conviction of the accused".

"Facts and circumstances of the case show that the woman was mature enough to fully understand what was happening between the two.

"Her consent for physical relationship before marriage was an act of her conscious decision. She was also married with the accused and gave birth to a female child...Her testimony is not intrinsic worth believing to base conviction of the accused," Additional Sessions Judge Sanjiv Jain said.

The judge further said "the woman made material improvements in her testimony and also concealed the factum of her nikahnama(wedding) with the accused in her complaint which go to the root of the case."

The court acquitted the accused of the offences of rape, cheating and criminal intimidation under the IPC.

According to the prosecution, the accused proposed her for marriage and both started living together in south Delhi in 2011.

After nine months, she found out that the man was married and had three children and that he was kicked out of the house by the man's brothers, it alleged.

She lodged a complaint in 2012 but the police did not take action, it said, adding that she moved the court then following which the man was arrested on June 26, 2013.

The accused denied the allegations and claimed he married the complainant before having physical relations with her. He also contended that he had told the woman about his first wedlock before marrying her.